The present invention relates to a method and apparatus for automatically determining the boundaries between fractions in a fractionated sample and to a method and apparatus for automatically extracting fractions from a fractionated sample and in particular to such a method and apparatus wherein the fractionated sample is a fractionated blood sample.
Blood samples are often analysed or processed by fractionation to separate particular components. This allows particular components of interest to be extracted from a sample. Fractionation is achieved by centrifugation of the sample, which results in a sample having a number of layers or fractions, each fraction consisting of particular components of the blood. Typically, the centrifuged sample comprises three fractions, the uppermost fraction containing (amongst other components) plasma, the lowermost fraction containing (amongst other components) red blood cells and the middle fraction, known as the ‘buffy coat’, containing (amongst other components) white blood cells.
The fractions are typically extracted in turn by a pipette means under manual control. The fraction containing the component of interest is retained and the other fractions may be retained or disposed of as desired. Manually controlled extraction in this manner is time consuming and expensive. It is also requires considerable skill as, to the naked eye, the boundaries between fractions can be difficult to distinguish. These problems are exacerbated if the ‘buffy coat’ is the fraction of interest, for instance if DNA analysis of the sample is required, as the buffy coat is typically relatively thin in relation to the other fractions.
It is therefore an object of the present invention to provide a method and apparatus for automating some or all of this process.